Is it possible to make a D type flip flop without a clock input? How would one set the logic to 0 or 1 without using a clock input? Thank you.
A reasonable question... Congratulations for the insight! I always ask my students when considering flip-flops, "Is it possible to make an asynchronous D flip-flop?" I have also asked this question in the RG forum. Here is my explanation why it is not possible...
Bistable circuits with memory (latches, flip-flops, RAM cells...) are toggled by two different input signals - to set the circuit to "1" and "0". They must be applied only for a short time... and then the input sources must be disconnected... like in S&H circuit.
Another life analogy is the ordinary toggle switch. Once you press it (to turn the lamp on or off) then you have to release it, right?
This can be made in two ways - by two inputs or by one input and clock. The former is implemented in asynchronous RS latches where there is a "neutral" input combination (two ones for NAND latches and two zeros for NOR latches). The latter is implemented in synchronous D flip-flops by level or edge-triggered clock.
Another well-known analogy is the electric switch for lighting. Once you press it (to turn the lamp on or off) then you have to release it, right?
So, the role of the clock is to provide momentarilly acting input signals. In the case of the asynchronous D flip-flop, there is no "neutral" input state when the input source is disconnected. So it is not possible to make a D type flip-flop without a clock input.
"Do you think it would be possible if the output Q or ‘Q was fed into the clock input?"
A similar way is to make T flip-flop from D flip-flop - by connecting the inverted output to D input and using the clock as an input. However, the new T flip-flop is asyncronous.